The present invention relates to aerial cargo delivery systems and more particularly to a tow plate used in a low altitude parachute extraction system (LAPES).
A search of the prior art failed to uncover any prior art references which disclose an aerial cargo delivery system employing the tow plate of the present invention. A number of patents were uncovered which disclose various aerial delivery equipment, including tow plate devices, for use in systems for aerial delivery of cargo, such as LAPES, and platform aerial delivery systems (PADS). The following is a listing of the patents uncovered during the aforementioned search:
______________________________________ U.S. Pat. No. Patentee Issue Date ______________________________________ 3,257,089 Samms 6/21/66 3,398,917 Grabe 8/27/68 3,401,905 Rohrlick 9/17/68 3,424,410 Galaup 1/28/69 3,425,739 Frost et al 2/4/69 3,642,235 Criley et al 2/15/72 3,670,999 Leger 6/20/72 3,724,788 Petry et al 4/3/73 3,781,055 Keich et al 12/25/73 3,801,051 Hosterman et al 4/2/74 3,865,333 Fielding et al 2/11/75 4,241,890 Pearson 12/30/80 4,303,213 Bolender et al 12/1/81 British Patent No. 972,546; 10/14/64 French Patent No. 1,234,282; 10/17/60 French Patent No. 2,357,419; 2/3/78
The low altitude parachute extraction system (LAPES) is the most accurate and versatile method of aerial cargo delivery. It may be used to deliver most types of cargo with pinpoint precision and minimum expense from a cargo aircraft having a rear-opening cargo compartment, such as the C-130 Hercules, C-212 Aviocar, DHC-4 Caribou and DHC-5 Buffalo. The most notable distinction between the LAPES system and the PADS system is that no recovery parachutes are employed in the LAPES system.
According to the LAPES method, upon approach to the cargo extraction zone, a drogue parachute, which is usually attached to a tow plate clevis, is deployed from the rear opening of the aircraft cargo compartment. When the extraction zone is reached, the aircraft descends to a delivery height of about 5-10 ft. above the ground and the drogue parachute is deployed. Upon activation of the tow plate control, the force of the inflated drogue parachute is transferred, via an extraction clevis, to the extraction parachute(s) which, in turn, pulls the load platform from the aircraft rear opening.
The platform contacts the ground and decelerates to a stop under the combined forces of ground friction and the drag of the extraction parachute(s). In the event a LAPES aerial delivery is aborted for any reason prior to extraction of the cargo, means are provided for jettisoning the drogue parachute.
Of the above-listed patents, U.S. Pat. Nos. 3,801,051 and 4,303,213 to Hosterman et al and Bolender et al, respectively, disclose tow plates intended for use in a LAPES aerial delivery system of the type contemplated for the present invention. As explained in the Bolender et al patent, the capability of a tow plate device to rapidly, reliably and safely jettison the drogue parachute, as well as release the extraction clevis, is of critical importance in accomplishing a LAPES aerial delivery mission.
One of the difficulties inherent in the LAPES cargo delivery method is the existence of a large drag force which is transferred from the inflated drogue parachute to the extraction clevis and the drogue jettison mechanism. That drag force creates substantial frictional forces between the movable release components of the tow plate, which frictional forces must be overcome to effect operation of either the extraction clevis or the drogue jettison mechanism.
While some measure of improvement has been made in reducing the detrimental effect on the reliability and safety of the LAPES system caused by the aforementioned difficulties, further improvement is needed in the reduction of the frictional forces which are detrimental to reliable operation of the release components. In addition, the tow plate and clevis structures heretofore in use are of large, bulky or relatively complex construction and employ various configurations of roller bodies and curved surfaces intended to reduce the effects of the frictional forces transmitted from the drogue parachute. Moreover, the roller bodies of those tow plates are mounted directly upon their support shafts and constitute friction bearing mountings.